In an air damper described in Patent Document 1 (Japanese Patent Publication No. H08-105481), there is provided a piston movable inside the cylinder. Then, in the piston, there is formed an orifice allowing air in the air chamber inside the cylinder to flow in and out.
Moreover, in a concave portion formed in an outer peripheral surface of the piston, there is disposed an O-ring sealing the piston and an inner peripheral surface of the cylinder. Then, on a bottom surface of the concave portion, there is provided an air passage which is closed by the O-ring rolling toward one direction inside the concave portion by a friction force with the inner peripheral surface of the cylinder when the piston is pulled out of the cylinder, and which is opened by the O-ring rolling toward the other direction inside the concave portion by the friction force with the inner peripheral surface of the cylinder when the piston is pushed into the cylinder.
Due to the structure, when the piston is pulled out of the cylinder, a damping force by the air damper is exerted, and when the piston is pushed into the cylinder, the damping force by the air damper diminishes.